The present invention relates to a liquid crystal display device and a defect repairing method for the same.
Recently, liquid crystal display devices have been practically used in the fields of OA equipment and AV equipment owing to their advantages in compactness, small weight and size and small consumption power. In particular, an active matrix liquid crystal display device including a switching element (active device) in each picture element is capable of producing a fine dynamic display and hence is used as a display for a variety of equipment.
In an active matrix liquid crystal display device, picture elements are composed of picture element electrodes provided in the form of a matrix, a counter electrode opposing the picture element electrodes and a liquid crystal layer disposed therebetween. Each of a plurality of picture elements is controlled in its display state in accordance with an electric signal supplied through the switching element.
In an active matrix liquid crystal display device, short-circuit may be caused between the picture element electrode and the counter electrode or the like due to a conducting debris mixed in the liquid crystal layer. A normal voltage cannot be applied to a picture element in which the short-circuit through the picture element electrode is caused, resulting in a display defect that desired display cannot be obtained.
As a method for repairing a display defect, Japanese Laid-Open Patent Publication No. 4-178622 discloses a defect repairing method in which a photoresist including a black pigment is applied on the face of a glass substrate and a shield film is formed by exposing and curing a portion of the photoresist positioned on merely a picture element suffering from a display defect, so as to change a bright defect into an opaque point (dark defect). An dark defect is less visually recognized than a bright defect and hence merely slightly affects the display quality.
The present inventors have, however, found that a display defect cannot be effectively repaired by the defect repairing method disclosed in Japanese Laid-Open Patent Publication No. 4-178622.
In the defect repairing method of Japanese Laid-Open Patent Publication No. 4-178622, the entire picture element suffering from a bright defect is covered with a shield film formed so as to change the entire picture element into an opaque point, and therefore, the entire picture element having the display defect cannot make contribution to the display.
The present invention was devised in consideration of the aforementioned conventional problem, and an object is providing a liquid crystal display device capable of repairing a display defect without sacrificing an entire picture element having the display defect and providing a defect repairing method employed in the liquid crystal display device.
The object is achieved by first and second liquid crystal display devices and defect repairing methods for these devices described below.
The first liquid crystal display device of this invention includes a first substrate; a second substrate; a liquid crystal layer disposed between the first substrate and the second substrate; a plurality of picture element regions for producing a display; and in each of the plurality of picture element regions, a picture element electrode provided on a face of the first substrate facing the liquid crystal layer and a switching element electrically connected to the picture element electrode, and the picture element electrode includes a plurality of sub-picture element electrodes and a plurality of contact portions each for mutually electrically connecting at least some of the sub-picture element electrodes, and at least one of the plurality of sub-picture element electrodes is electrically connected to the switching element via a plurality of connection paths. Thus, the aforementioned object can be achieved.
The first liquid crystal display device preferably further includes a counter electrode provided on the second substrate and opposing the picture element electrode with the liquid crystal layer sandwiched therebetween, and preferably, the picture element electrode is composed of a solid portion including the plurality of sub-picture element electrodes and the plurality of contact portions, and a plurality of openings, and in each of the plurality of picture element regions, the liquid crystal layer is formed into a plurality of liquid crystal domains each in a radially-inclined orientation state correspondingly to the plurality of openings and the solid portion by inclined electric fields generated at respective edge portions of the plurality of openings of the picture element electrode when a voltage is applied between the picture element electrode and the counter electrode, whereby producing a display by changing orientation states of the plurality of liquid crystal domains in accordance with the applied voltage.
Preferably, at least some of the plurality of openings have substantially the same shape and the same size, and form at least one unit lattice arranged so as to have rotational symmetry.
Preferably, each of the at least some of the plurality of openings is in a rotationally symmetrical shape.
Alternatively, each of the at least some of the plurality of openings may be in a substantially circular shape.
Each region of the solid portion surrounded with the at least some of the plurality of openings may be in a substantially circular shape.
Preferably, in each of the plurality of picture element regions, a total area of the plurality of openings of the picture element electrode is smaller than an area of the solid portion of the picture element electrode.
The liquid crystal display device preferably further includes a protrusion within each of the plurality of openings, and preferably, a cross-sectional shape of the protrusion taken in a plane direction of the substrate is the same as a shape of the corresponding opening, and a side face of the protrusion has orientation-regulating force for orienting liquid crystal molecules of the liquid crystal layer in the same direction as an orientation-regulating direction obtained by the inclined electric field.
In the first defect repairing method for a liquid crystal display device of this invention, the liquid crystal display device includes a first substrate; a second substrate; a liquid crystal layer disposed between the first substrate and the second substrate; a plurality of picture element regions for producing a display; and in each of the plurality of picture element regions, a picture element electrode provided on a face of the first substrate facing the liquid crystal layer and a switching element electrically connected to the picture element electrode, the picture element electrode being composed of a plurality of sub-picture element electrodes and a plurality of contact portions for mutually electrically connecting at least some of the plurality of sub-picture element electrodes, and at least one of the plurality of sub-picture element electrodes being electrically connected to the switching element via a plurality of connection paths, and the defect repairing method includes the steps of specifying a picture element region having a display defect among the plurality of picture element regions and specifying a sub-picture element electrode suffering from short-circuit among the plurality of sub-picture element electrodes in the specified picture element region; and electrically disconnecting the specified sub-picture element electrode from the switching element with keeping electrical connection between the at least one of the plurality of sub-picture element electrodes and the switching element by cutting off a contact portion connected to the specified sub-picture element electrode among the plurality of contact portions. Thus, the aforementioned object can be achieved.
The second liquid crystal display device of this invention includes a first substrate; a second substrate; a liquid crystal layer disposed between the first substrate and the second substrate; a plurality of picture element regions for producing a display; and in each of the plurality of picture element regions, a picture element electrode provided on a face of the first substrate facing the liquid crystal layer and a switching element electrically connected to the picture element electrode, and the picture element electrode includes a plurality of sub-picture element electrodes electrically connected to the switching element in parallel. Thus, the aforementioned object can be achieved.
In the second defect repairing method for a liquid crystal display device of this invention, the liquid crystal display device includes a first substrate; a second substrate; a liquid crystal layer disposed between the first substrate and the second substrate; a plurality of picture element regions for producing a display; and in each of the plurality of picture element regions, a picture element electrode provided on a face of the first substrate facing the liquid crystal layer and a switching element electrically connected to the picture element electrode, and the picture element electrode including a plurality of sub-picture element electrodes electrically connected to the switching element in parallel, and the defect repairing method includes the steps of specifying a picture element region having a display defect among the plurality of picture element regions and specifying a sub-picture element electrode suffering from short-circuit among the plurality of sub-picture element electrodes in the specified picture element region; and electrically disconnecting the specified sub-picture element electrode from the switching element with keeping electrical connection between the plurality of sub-picture element electrodes other than the specified sub-picture element electrode and the switching element. Thus, the aforementioned object can be achieved.
The functions of the present invention are as follows:
In the first liquid crystal display device of this invention, at least one of the plurality of sub-picture element electrodes is electrically connected to the switching element via a plurality of connection paths. At this point, a connection path for electrically connecting the sub-picture element electrode to the switching element includes any of the other sub-picture element electrodes and the contact portions. Accordingly, in the case where a short-circuit defect is caused in a sub-picture element electrode included in one connection path among the plurality of connection paths for connecting a given sub-picture element electrode to the switching element, the sub-picture element electrode having the short-circuit defect can be electrically disconnected from the switching element with keeping the electrical connection between the given sub-picture element electrode and the switching element by cutting off a contact portion. Therefore, a voltage can be normally applied to the given sub-picture element electrode through the switching element, resulting in attaining sufficient display quality.
Also, in a preferred embodiment of the liquid crystal display device of this invention, the picture element electrode is composed of a solid portion (a region of the picture element electrode other than openings where a conducting film is present) including a plurality of sub-picture element electrodes and a plurality of contact portions, and a plurality of openings (a region of the picture element electrode where no conducting film is present). The solid portion is typically formed from a continuous conducting film. The liquid crystal layer is in a vertical orientation state when no voltage is applied, and is formed into a plurality of liquid crystal domains each in a radially-inclined orientation state owing to inclined electric fields generated at the edge portions of the openings of the electrode when a voltage is applied. Typically, the liquid crystal layer is made from a liquid crystal material having negative dielectric anisotropy and is controlled in its orientation by vertical alignment layers sandwiching the liquid crystal layer.
The liquid crystal domains formed by the inclined electric fields are respectively formed in regions corresponding to the openings and the solid portion of the electrode, and a display is produced by changing the orientation states of the liquid crystal domains in accordance with the applied voltage. Since each of the liquid crystal domains is in an axially symmetrical orientation, the viewing angle dependency of display quality is reduced, resulting in attaining a wide viewing angle characteristic.
Furthermore, since the liquid crystal domain corresponding to the opening and the liquid crystal domain corresponding to the solid portion are formed owing to the inclined electric fields generated at the edge portions of the openings, these liquid crystal domains are formed adjacently and alternately, and the orientations of liquid crystal molecules of the adjacent liquid crystal domains are substantially continuous. Accordingly, no disclination line is formed between the liquid crystal domain corresponding to the opening and the liquid crystal domain corresponding to the solid portion, the display quality can be prevented from lowing due to a disclination line, and the orientation of the liquid crystal molecules is highly stable.
In this liquid crystal display device, the liquid crystal molecules are placed in the radially-inclined orientation state not only in the region corresponding to the solid portion of the electrode but also in the region corresponding to the opening. Therefore, the orientation of the liquid crystal molecules is highly continuous and a stable orientation state can be realized, resulting in displaying an even display free from unevenness. In particular, it is necessary to apply the inclined electric field for controlling the orientation of the liquid crystal molecules to a large number of liquid crystal molecules for realizing a good response characteristic (a high response speed), and for this purpose, it is necessary to form a large number of openings (edge portions). In the liquid crystal display device of this invention, since the liquid crystal domains having the stable radially-inclined orientation are formed correspondingly to the openings, and hence, even when a large number of openings are formed for improving the response characteristic, the lowering of the display quality (occurrence of unevenness) derived from the increased number of openings can be avoided.
When at least some of the plurality of openings are formed in substantially the same shape and the same size so as to form at least one unit lattice arranged to have rotational symmetry, the plurality of liquid crystal domains can be highly symmetrically arranged by using the unit lattice as a unit, resulting in improving the viewing angle dependency of the display quality. Furthermore, when the entire picture element region is divided into unit lattices, the orientation of the liquid crystal layer can be stabilized over the entire picture element region. For example, the openings are arranged so that the centers of the respective openings can form a square lattice. In the case where one picture element region is divided by an opaque composing element such as an storage capacitance line, the unit lattices are arranged at least in each region distributing the display.
When each of at least some of the plurality of openings (typically, the openings forming a unit lattice) is formed in a rotationally symmetrical shape, the radially-inclined orientation of the liquid crystal domain formed correspondingly to the opening can be stabilized. For example, each of the openings is formed in the shape (seen from the substrate normal direction) of a circle or regular polygon (such as a square). The opening may be in a shape not rotationally symmetrical (such as an ellipse) depending upon the shape (the ratio between the width and the length) of the picture element. Furthermore, when a region of the solid portion substantially surrounded with the openings (xe2x80x9ca unit solid portionxe2x80x9d described below) is in a rotationally symmetrical shape, the stability of the radially-inclined orientation of the liquid crystal domain formed correspondingly to the solid portion can be improved. For example, in the case where the openings are disposed in a square lattice arrangement, the opening may be formed in a substantially star-shape or cross-shape with the unit solid portion formed in a substantially circular shape or substantially square shape. Needless to say, the opening and the region of the solid portion substantially surrounded with the openings may be both formed in a substantially square shape.
In order to stabilize the radially-inclined orientation of the liquid crystal domain formed correspondingly to the opening of the electrode, the liquid crystal domain corresponding to the opening is preferably formed in a substantially circular shape. Conversely speaking, the shape of the opening is designed so that the liquid crystal domain corresponding to the opening can be formed in a substantially circular shape.
Needless to say, in order to stabilize the radially-inclined orientation of the liquid crystal domain corresponding to the solid portion of the electrode, the region of the solid portion substantially surrounded with the openings is preferably formed in a substantially circular shape. One liquid crystal domain formed in the solid portion made from a continuous conducting film is formed correspondingly to the region of the solid portion substantially surrounded with the plural openings (unit solid portion). Accordingly, the shape and the arrangement of the openings are determined so that the region of the solid portion (unit solid portion) can be formed in a substantially circular shape.
In any of the aforementioned cases, the total area of the openings formed in the electrode is preferably smaller than the area of the solid portion in each picture element region. As the area of the solid portion is larger, the area (defined on a plane seen from the substrate normal direction) of a region of the liquid crystal layer directly affected by the electric fields generated by the electrodes is larger. Therefore, the optical characteristic (such as transmittance) of the liquid crystal layer against voltage can be improved.
It is preferably determined whether the opening is formed in a substantially circular shape or the unit solid portion is formed in a substantially circular shape depending upon in which structure the area of the solid portion can be larger. It is appropriately selected which structure is preferred depending upon the pitch of picture elements. Typically, in the case where the pitch exceeds approximately 25 xcexcm, the openings are preferably formed so as to form substantially circular unit solid portions, and in the case where the pitch is smaller than approximately 25 xcexcm, the opening is preferably formed in a substantially circular shape.
The orientation-regulating force caused by the inclined electric fields generated at the edge portions of the openings of the electrode works merely under voltage application. Therefore, when, for example, an external force is applied to the liquid crystal panel under application of no voltage or a comparatively low voltage, the radially-inclined orientation of the liquid crystal domain sometimes cannot be kept. In order to overcome this problem, in one preferred embodiment, the liquid crystal display device includes a protrusion within the opening of the electrode and having an orientation-regulating force for orienting the liquid crystal molecules of the liquid crystal layer in the same direction as the orientation-regulating direction obtained by the inclined electric field. The cross-sectional shape of the protrusion taken in a plane direction of the substrate is the same as the opening, and is preferably in a rotationally symmetrical shape similarly to the shape of the opening.
In the aforementioned liquid crystal display device, merely by forming openings in the picture element electrode, stable radially-inclined orientation can be realized. Specifically, the present liquid crystal display device can be fabricated by a known fabrication method merely by modifying a photomask used in patterning a conducting film into a pattern of picture element electrodes so as to form openings in a desired shape in desired arrangement.
In the second liquid crystal display device of this invention, the plurality of sub-picture element electrodes are electrically connected to the switching element in parallel. Accordingly, in the case where short-circuit is caused between a given sub-picture element electrode and the counter electrode, merely the sub-picture element electrode suffering from the short-circuit defect can be electrically disconnected from the switching element with keeping the electrical connection between the other sub-picture element electrodes and the switching element. Therefore, a normal voltage is applied to the other sub-picture element electrodes through the switching element, resulting in obtaining sufficient display quality.